1. Field of the Invention
The present invention relates to a method and apparatus for hysteresis control.
2. Description of the Related Art
As an example of a hysteresis control apparatus, one disclosed in the Unexamined Japanese Patent Publication No. 8-115068 (see paragraph numbers 0009 to 0020, FIG. 1 to FIG. 3) is known. An overview of the hysteresis control apparatus will be explained with reference to FIG. 1 below. FIG. 1 is a block diagram showing an example of the configuration of a conventional hysteresis control apparatus.
The hysteresis control apparatus shown in FIG. 1 is provided with a first signal comparator 801 that compares a relationship in magnitude between an input signal value and set value (input signal value>set value), a second signal comparator 802 that compares a relationship in magnitude between an input signal value and set value (input signal value<set value), a control circuit 803 that processes the comparison results at the first signal comparator 801 and second signal comparator 802 and a signal switching circuit 804 that outputs the output value of the control circuit 803 with a hysteresis characteristic added thereto.
It should be noted here that, for example, in a mobile communication system, transmit power control is performed to solve a near-far problem. This transmit power control involves a plurality of control sections, each of which constitutes an input value operating variation width. FIG. 2 is a time chart illustrating a control mode which is assumed when hysteresis control is performed using the hysteresis control apparatus shown in FIG. 1 in such a control system having a plurality of control sections.
FIG. 2 shows four control sections a, b, c and d. The control section a is an input value operating variation width including a hysteresis control section A. The control section b is an input value operating variation width including hysteresis control sections A and B. The control section c is an input value operating variation width including hysteresis control sections B and C. The control section d is an input value operating variation width including the hysteresis control section C.
In the hysteresis control section A, a comparison is made at a maximum value in the control section a and a minimum value in the control section b to decide whether or not to make a transition to the neighboring control section. In the hysteresis control section B, a comparison is made at a maximum value in the control section b and a minimum value in the control section c to decide whether or not to make a transition to the neighboring control section. In the hysteresis control section C, a comparison is made at a maximum value in the control section c and a minimum value in the control section d to decide whether or not to make a transition to the neighboring control section.
However, according to the hysteresis control method using the above described conventional hysteresis control apparatus, it is necessary to perform two comparisons in the hysteresis control sections and change the set values until control values (output values) in the control sections to which a transition is to be made are obtained. Furthermore, there is a problem that in order to know a variation in a control section, it is not possible to detect an input value variation width extending over the control sections unless a difference from the immediately preceding control section is calculated after a desired control value is determined.